1. Field of the Invention
The present disclosure relates to fluorescent sulfonyl ureido benzoxazinone pigments and a process for preparing the same. More particularly, the present disclosure relates to fluorescent sulfonyl ureido benzoxazinone pigments that are colorless. The benzoxazinone pigments may be used in ink compositions in a wide variety of printing systems, such as inkjet printing systems, and are particularly well-suited for security applications.
2. Description of the Related Art
Fluorescent pigments emitting in the yellow-green region are well known. However, for many applications, such as security-related applications, colorless pigments, which fluoresce in the visible region, are needed. For instance, some well-known fluorescent pigments, such as fluorescein, rhodamine, and coumarin, have an appearance and color under normal lighting conditions that are not desirable for certain security applications and printing systems. Another desirable characteristic of fluorescent pigments is to maintain lightfastness over a length of time after their application to a substrate.
Benzoxazinone compounds are colorless, fluorescent pigments that are the state of the art. See, e.g., EP 0 314 350. However, the preparation of these compounds involves a multi-step synthesis or a one-step process that generates a large amount of non-environmentally friendly waste. For example, benzoxazinone compounds may be prepared by reacting an aromatic sulfonyl chloride with anthranilic acid in pyridine as solvent and as base; however, during the work up, water is added and the pyridine reactant cannot be recycled easily, producing non-environmentally friendly waste. In addition, purification by column chromatography or recrystallization with methylene chloride is often necessary with this process, producing an additional source of non-environmentally friendly waste. Therefore, a need exists in the art for more colorless compounds that brightly fluoresce in certain emission wavelengths under UV irradiation, and a process for preparing such compounds that is commercially practical and environmentally friendly.